Update changelog

Author: MetRonnie

CHANGES.md

@@ -10,6 +10,14 @@ creating a new release entry be sure to copy & paste the span tag with the
 `actions:bind` attribute, which is used by a regex to find the text to be
 updated. Only the first match gets replaced, so it's fine to leave the old
 ones in. -->
+-------------------------------------------------------------------------------
+## __cylc-ui-1.6.0 (<span actions:bind='release-date'>Upcoming</span>)__
+
+### Enhancements
+
+[#1187](https://github.com/cylc/cylc-ui/pull/1187) - Improved the workflow
+filtering menu in the sidebar.
+
 -------------------------------------------------------------------------------
 ## __cylc-ui-1.5.0 (<span actions:bind='release-date'>Released 2023-02-20</span>)__